The standard wheel loaders are equipped with an engine as its driving source and has engine power transmitted to the wheels via a torque converter or a gear transmission. In response to operators' manipulation of the forward/reverse lever, the wheel loader allows the gear transmission to be shifted to forward (F), to neutral (N), or to reverse (R). The wheel loaders are also furnished with a parking brake device. Activating the parking brake causes the wheel loaders to put the gear transmission in the neutral (N) position to cut off power transmission to the wheels. This operation prevents the parking brake from dragging and inhibits the wheel loader from getting started inadvertently.
By contrast, electric driving wheel loaders have their wheels driven by the motor. Since the motor itself can be changed in its driving direction and possesses a variable speed function, some vehicles of this type are not equipped with the gear transmission. That means there is a need for some other methods for cutting off power transmission to the wheels while the parking brake is being activated. A first known method, for example, involves an electric vehicle parking brake device having a parking brake lever that is equipped with a switch for causing a motor controller to detect the operating status of the parking brake on the vehicle, the switch controlling the output of power conversion means in the motor controller (e.g., see Patent Literature 1). A second known method involves an electric vehicle parking brake device having a lock detection device that detects the condition of engagement between the locking teeth of a parking gear attached to the motor output shaft; and the pawls of a locking member, the lock detection device having a controller detecting the operating status of the parking brake of the vehicle and operating a relay switch accordingly to disconnect a power supply circuit of the motor (e.g., see Patent Literature 2).